AssafL
Head-Fier
- Joined
- Jun 21, 2002
- Posts
- 61
- Likes
- 0
As I am new to Head-fi, please forgive me if this issue has already been discussed.
I recently purchased the Stax In-the-earspeakers. Others have described the sound of these, which is remarkable (especially at this price range - see driftwood's detailed review elsewhere).
At first, I used alkaline batteries. Pretty soon (and with a pile of exhausted alkaline cells to show for it), this became too expensive so I tried 2 NiMH cells. Sound quality deteriorated considerably.
It became clear that the Stax driver unit needs a higher voltage for optimal performance. Performance at 4.5V (using a wall wart) was spectacular, 3V provided ample performance, but 2.4V was lacking.
Rummaging around the neighborhood Radio-Shack, I came across a unit called a "power bank - NiMH charger). The unit is a 4 cell NiMH charger, Wall-wart and DC-DC converter, all in one sleek unit. $39 was a bit steep but I ended up taking the unit home. 4 NiMH cells later, I set the power bank to 4.5 and plugged the Stax into the power bank.
The Stax started charging the internal voltage doublers (the power up "squeal"), and after a second or so the power bank abruptly shut itself down. I tried different combinations (DC-DC, wall wart mode), all with the same effect. Setting the voltage at 3V solved the problem, but I wanted 4.5V performance!
Radio-shack replaced the unit, but the new unit had the same problem. It was time to take out the test equipment. The problem became clear: at 4.5V, the power up current draw of the Stax driver, is a whopping 1.5A (for 2 seconds)! As the power bank has an automatic shut down at 1A, it would shut itself off.
I have identified two solutions (that work):
1. Start at 3V and switch to 4.5V (requires a screwdriver)
2. Pulse the power until the Stax has enough charge (unfortunately, the power bank does not have a power switch and the only way to reset the over-current sensor is to disconnect the DC cord).
The third option was to disable (or desensitize) the current overload sensing circuit so I opened the charger. Its construction, faithful to the brand, it is rather messy, with complicated switching circuitry (240/110AC, DC to DC, charging sensors), glued components, RFI shielding foil, all cramped in a small enclosure.
Does anyone have a schematic of the charger (or knows how to get one)?
Thanks,
AssafL.
I recently purchased the Stax In-the-earspeakers. Others have described the sound of these, which is remarkable (especially at this price range - see driftwood's detailed review elsewhere).
At first, I used alkaline batteries. Pretty soon (and with a pile of exhausted alkaline cells to show for it), this became too expensive so I tried 2 NiMH cells. Sound quality deteriorated considerably.
It became clear that the Stax driver unit needs a higher voltage for optimal performance. Performance at 4.5V (using a wall wart) was spectacular, 3V provided ample performance, but 2.4V was lacking.
Rummaging around the neighborhood Radio-Shack, I came across a unit called a "power bank - NiMH charger). The unit is a 4 cell NiMH charger, Wall-wart and DC-DC converter, all in one sleek unit. $39 was a bit steep but I ended up taking the unit home. 4 NiMH cells later, I set the power bank to 4.5 and plugged the Stax into the power bank.
The Stax started charging the internal voltage doublers (the power up "squeal"), and after a second or so the power bank abruptly shut itself down. I tried different combinations (DC-DC, wall wart mode), all with the same effect. Setting the voltage at 3V solved the problem, but I wanted 4.5V performance!
Radio-shack replaced the unit, but the new unit had the same problem. It was time to take out the test equipment. The problem became clear: at 4.5V, the power up current draw of the Stax driver, is a whopping 1.5A (for 2 seconds)! As the power bank has an automatic shut down at 1A, it would shut itself off.
I have identified two solutions (that work):
1. Start at 3V and switch to 4.5V (requires a screwdriver)
2. Pulse the power until the Stax has enough charge (unfortunately, the power bank does not have a power switch and the only way to reset the over-current sensor is to disconnect the DC cord).
The third option was to disable (or desensitize) the current overload sensing circuit so I opened the charger. Its construction, faithful to the brand, it is rather messy, with complicated switching circuitry (240/110AC, DC to DC, charging sensors), glued components, RFI shielding foil, all cramped in a small enclosure.
Does anyone have a schematic of the charger (or knows how to get one)?
Thanks,
AssafL.
